Process for purifying hexamethylenediamine

Abstract

Hexamethylenediamine (HMD) is purified by dissolving ammonia in crude molten HMD under pressure, directing the solution thus prepared to a reduced pressure zone where the ammonia is vaporized thereby causing a portion of the HMD to crystallize following which the crystals in the slurry are washed with essentially pure HMD. This purified HMD is suitable for conversion into polyamide fibers.

We claim: 
     
       1. A process for the purification of hexamethylenediamine which comprises absorbing substantially anhydrous ammonia in molten crude hexamethylenediamine in a first zone, volatilizing a portion of the dissolved ammonia in a second zone to cool and thereby crystallize at least a portion of the hexamethylenediamine, separating the crystalline hexamethylenediamine from the molten hexamethylenediamine in a third zone, and thereafter washing the thus obtained crystalline diamine with refined molten hexamethylenediamine. 
     
     
       2. The process of claim 1 wherein the ammonia which is volatilized in the second zone is recycled to the first zone. 
     
     
       3. The process of claim 1 wherein molten crude hexamethylenediamine feed is introduced into the third zone and contacted with said crystalline hexamethylenediamine. 
     
     
       4. The process of claim 3 wherein the impurities are removed from the process along with a portion of the molten hexamethylenediamine from the third zone. 
     
     
       5. A process for the purification of hexamethylenediamine which comprises absorbing substantially anhydrous ammonia in molten crude hexamethylenediamine in a first zone, volatilizing a portion of the dissolved ammonia in a second zone to cool and thereby crystallize at least a portion of the hexamethylenediamine, separating the crystalline hexamethylenediamine from the molten hexamethylenediamine in a third zone, displacement washing the thus obtained crystalline diamine with refined molten hexamethylenediamine counter-currently in a fourth zone, recycling at least a portion of the diamine used to wash the crystals to said first zone, melting the washed crystals of hexamethylenediamine to provide the said refined hexamethylenediamine wash and thereafter recovering that portion of the melted crystals of hexamethylenediamines which are not used for said wash. 
     
     
       6. The process of claim 5 wherein the ammonia which is volatilized in the second zone is recycled to the first zone. 
     
     
       7. The process of claim 5 wherein molten crude hexamethylenediamine feed is introduced into the third zone and contacted with said crystalline hexamethylenediamine. 
     
     
       8. The process of claim 7 wherein the impurities are removed from the process along with a portion of the molten hexamethylenediamine from the third zone.